I think that the Hemingway App is useful as a guide to highlight parts that one might need to reconsider, but like some have said: do not rely on it too much. Different people have different writing styles and flairs, which the program may not be able to pick up well. I put some of my writing into the site, and the result told me my style is too sophisticated and difficult to understand (on average of grade 11 and above). Then when I ran text excerpts of well-known writers - like Tolkien's LOTR - and the guy really love his adverbs. /shrugs

Since this question went unanswered the first time I asked, so let's try again: has anyone tried to use MS Notes? I stopped using it for personal projects and reserve that for school note-taking now; it's quite similar to Evernote.